1. Field of the Invention
The present invention relates to a large capacity sheet feeding apparatus having an intermediate conveying device that feeds a sheet on which an image is to be formed to an image-forming apparatus, such as a copying machine, a printing press, a facsimile machine, a printer, a plotter, and the like.
2. Discussion of the Background
In any image forming apparatus, such as a copying machine, a facsimile machine, various kinds of printers, such as a printing press, a mimeographic printer, an ink-jet printer, or the like, and a plotter, the printer, more particularly a mimeographic printer or an offset printer, is often called upon to produce a large amount of prints. This is because, unlike the case of a copying machine, a master, i.e., a plate that is made with an image of an original document is used and the master allows producing a great number of prints. There are many cases in which even several thousands of prints from the original document are produced if required.
It is assumed that a large capacity sheet feeding apparatus with an intermediate conveying device capable of feeding a large number of sheets on which an image will be formed must be mechanically connected to such an image forming apparatus as a printer or the like (See U.S. Pat. No. 5,441,247, for example).
The large capacity sheet feeding apparatus having an intermediate conveying device recited in the U.S. Pat. No. 5,441,247 is provided with a sheet stacking section having a large capacity sheet feeding tray capable of rising and lowering with at least several thousands of sheets stacked thereupon, a sheet feeding mechanism section that feeds the sheet while picking up the same in a sequential manner from the sheet stacking section, and an intermediate conveying device that conveys the sheet fed from the sheet feeding mechanism section to a main body sheet feeding tray of a sheet feeding section on a side of a main body of an image forming apparatus, or in the vicinity of a sheet feeding inlet where a main body sheet feeding device of the sheet feeding section faces.
The invention recited in the aforementioned U.S. Pat. No. 5,441,247 relates to an apparatus and method for feeding a paper sheet (a so-called cut sheet, and is hereinafter referred to as a sheet) that is stacked in, and picked up from a storage and fed to a high speed printing machine during its operation. According to the above-mentioned invention, the large capacity sheet feeding apparatus having the intermediate conveying device of the above-mentioned invention is responsive to a recent trend of increasing speed of printing machines and copying machines. In addition, the apparatus and method recited in the aforementioned invention are movable and applicable for various kinds of image forming apparatus, such as a printer or the like. Therefore, a large capacity sheet storage apparatus can be provided for a low price.
On the other hand, in the aforementioned various kinds of image forming apparatus, to which a large capacity sheet feeding apparatus having an intermediate conveying device is connected, specifically, in a mimeographic printing apparatus, the sheets of various kinds of sizes are used. Generally, in the sheet sizes for use in the mimeographic printing apparatus, ten kinds of sheet sizes are commonly used even the size of a postcard is taken off as described later.
In the mimeographic printing apparatus, a reproduced heat-sensitive mimeographic master is entrained about a circumferential face of a printing drum, or master drum, and the sheet which is fed from the sheet feeding section is pressed toward the circumferential face of the printing drum by a pressing device such as a pressing roller or a pressing drum. Ink is thereby exuded from an opening portion of the printing drum and perforations of a heat-sensitive mimeographic master. The ink is transferred to a sheet and printed image is thereby obtained.
However, in the technique disclosed in the aforementioned U.S. Pat. No. 5,441,247, even when the mimeographic printing apparatus and the large capacity sheet feeding apparatus having the intermediate conveying device are not electrically connected or not connected in a state capable of communicating with each other, namely, in a usually called “off line” mode, the printer can execute a printing operation with a sheet fed from the large capacity sheet feeding apparatus having an intermediate conveying device.
However, when a sheet smaller than the selected printed matter is mixed in with sheets of appropriate size on the large capacity sheet feeding tray a problem occurs when the mimeographic printing apparatus does not detect that the sheet is too small, and the image overhangs the size of the sheets. Further, when the ink is transferred to the pressing drum the overhanging image, larger than the aberrant sheet, results in ink applied to the drum and a press roller. The accumulated ink causes both sheet jamming and inappropriate printing on the rear surface of a sheet, which is fed after a preceding sheet stained with ink.
Furthermore, the ink put on the circumferential surface of the press roller and the printing drum accumulates and scatters or falls down. An inner part of the machine is thereby stained. Those are the problems of the aforementioned U.S. Pat. No. 5,441,247.
When a sheet of the size smaller than the reproducing and printing size is mixed in the sheets stacked on a sheet feeding tray on a side of the main body of the mimeographic printing apparatus, the problem similar to the above mentioned problem also exists. From other point of view, in a case that the mimeographic printing apparatus is not, even mechanically, connected to the large capacity sheet feeding apparatus having the intermediate conveying device, the problem similar to the above mentioned problem also occurs.
Accordingly, the inventors of the present invention noted that in a condition that the mimeographic printing apparatus and the large capacity sheet feeding apparatus having the intermediate conveying device are mechanically connected under a condition of communicating with each other, the intermediate conveying device is provided with a relatively long intermediate sheet conveying path for conveying sheets fed from a sheet feeding section one after another. The inventors proposed a sheet size detecting mechanism that detects the sheet size of the sheets fed from the sheet feeding mechanism, utilizing the long intermediate sheet conveying path, and the inventors thereby completed an invention which prevents a delivery of a sheet having a size different from the reproducing and printing size to the mimeographic printing apparatus, even when a sheet having the size different from reproducing and printing size is mixed to the sheets on the large capacity sheet feeding tray.
Therefore, the present invention is made in light of the above described problem and a main object of the present invention is to solve the above problem and to provide a novel large capacity sheet feeding apparatus having an intermediate conveying device being effectual as described later.